The present invention is concerned with a new and improved electrooptical instrument which can detect the presence of liquids, and also relates to a method of operating such electrooptical instrument.
Generally speaking, the electrooptical instrument of the present invention is of the type comprising at least one monochromatic infrared source, one light conductor which totally reflects infrared radiation at the surface of one end thereof, one infrared detector, and one electronic circuit for signal processing.
Instruments that perform this function are generally referred to as liquid sensing probes. A compact, practical unit is disclosed, for example, in Swiss Pat. No. 512,060 to which reference may be had and the disclosure of which is incorporated herein by reference, and which has a high sensitivity, is quite shock-proof, and requires no subsequent adjustments.
All of the liquid sensing probes known up to this time require relatively high-power light-emitting diodes in order to obtain a reproducible response. The use of instruments of this type is therefore forbidden in some countries for safety reasons, especially if they are employed in connection with highly explosive materials.